This application claims the benefit of Korean Application No. 2001-84397, filed Dec. 24, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein.
1. Field of the Invention
The present invention relates to microwave ovens, and more particularly, to a microwave oven which can suppress noise induced in a high-voltage line due to a use of an inverter.
2. Description of the Related Art
Generally, a microwave oven carries out a cooking operation by converting commercial alternating current (AC) power into a high voltage to drive a magnetron. Since the microwave oven uses the commercial AC power, it is difficult to install and use the microwave oven in transportation vehicles such as cars.
Recently, a microwave oven has been developed to use direct current (DC) power, such as a battery, to cook foods. This type of microwave oven employs an inverter circuit to convert a DC voltage into an AC voltage required to drive a magnetron.
FIG. 1 shows a convention microwave oven using DC power comprising a DC power source 1, a switching unit 2, an inverter unit 3, a high voltage transformer 4, a magnetron driving unit 5 and a magnetron filter box 6.
The magnetron filter box 6 includes choke coils 8 and feed-through condensers 9 installed therein, which constitute a low pass filter, to prevent fundamental waves of 2450 MHz, harmonic waves and noise generated by the driving of a magnetron 7, from radiating to the outside.
The high voltage transformer 4 includes primary and secondary coils L1 and L2 which induce a high voltage according to their turn ratio, and a heater coil L3 which supplies an AC voltage so as to have the magnetron 7 emit thermions.
In a conventional microwave oven using AC power for a home use, power of 3.3V AC 50/60 Hz is supplied through a high voltage line connected to a heater coil, and a magnetron emits thermions without any difficulty. However, in the conventional microwave oven using the DC power shown in FIG. 1, an inverter circuit is activated to drive the magnetron 7, and a high usable frequency of 20 to 50 KHz is obtained. Accordingly, an impedance value is also high. For this reason, although AC power of 3.3V AC 50/60 Hz is supplied, it is difficult to heat the magnetron 7 to a temperature high enough to emit thermions in the conventional microwave oven using the DC power source 1.
Therefore, to drive the magnetron 7, inductance of the choke coils 8 installed in the magnetron filter box 6 is lowered to supply an AC voltage of higher than 7V AC.
However, noise is widely generated while inducing high electrical energy in a secondary side of the high voltage transformer 4 using the inverter circuit. Furthermore, this noise is radiated to the outside as the AC voltage of a high frequency (20 to 50 KHz) is supplied to the magnetron 7 through a high voltage line connecting a heater coil in the secondary side of the high voltage transformer 4 to the magnetron 7.
Accordingly, it is an object of the present invention to provide a microwave oven which supplies DC power to a magnetron, thereby enabling noise induced in a high voltage line to be suppressed.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a microwave oven comprising a high voltage transformer having a high voltage line, a magnetron filter box connected to the high voltage line and comprises a magnetron and a filter circuit installed therein, and a direct current (DC) power supply unit which supplies DC power to the magnetron so as to suppress noise induced in the high voltage line.
According to an aspect of the present invention, the high voltage transformer includes a secondary side which generates alternating current (AC) power, and the DC power supply unit includes a rectifying unit which rectifies the AC power into the DC power. The rectifying unit includes a plurality of rectifying diodes, each having an anode and a cathode, connected in parallel to the secondary side of the high voltage transformer, wherein the anodes are connected to a heater coil of the high voltage line and the cathodes are connected to the magnetron.
According to another aspect of the present invention, the DC power supply unit includes a choke coil which forms ripples in the DC power so as to prevent a moding of the magnetron.